By virtue of such advantageous features as light weight, small thickness and low power consumption, liquid crystal display devices have been used in various fields as display devices of OA equipment, such as personal computers, and TVs. In recent years, liquid crystal display devices have also been used as display devices of portable terminal equipment such as mobile phones, car navigation apparatuses, game machines, etc.
In general, a liquid crystal display panel of a fringe field switching (FFS) mode or an in-plane switching (IPS) mode is configured such that a liquid crystal layer is held between an array substrate, which includes a pixel electrode and a common electrode, and a counter-substrate. In particular, in the FFS mode, liquid crystal molecules are rotated in a plane parallel to a substrate major surface, by a fringe electric field between the pixel electrode and the common electrode. Thereby, retardation (Δn·d; Δn is a refractive index anisotropy of the liquid crystal layer, and d is a cell gap for holding the liquid crystal layer) of the liquid crystal layer is varied.
When a liquid crystal material (positive-type liquid crystal material) with a positive dielectric constant anisotropy is applied to the liquid crystal layer, liquid crystal molecules are aligned such that their major axes are positioned along a fringe electric field. Thus, when a fringe electric field extending from the pixel electrode toward the common electrode is produced, liquid crystal molecules are raised along an electric field in the vertical direction (cell thickness direction) on the pixel electrode or slits, and a sufficiently high retardation cannot be obtained. Consequently, a modulation ratio per pixel lowers, and a high transmittance cannot be obtained.
On the other hand, when a liquid crystal material (negative-type liquid crystal material) with a negative dielectric constant anisotropy is applied to the liquid crystal layer, liquid crystal molecules are aligned such that their major axes are positioned perpendicular to the fringe electric field. Thus, even in the case of a vertical electric field, liquid crystal molecules are not easily raised, and a relatively high retardation can be maintained. Compared to the case of applying the positive-type liquid crystal material, a higher transmittance can be obtained. In the case where such a negative-type liquid crystal material is applied, there has been a demand for a further improvement in transmittance.